The present invention relates to a magnetic recording device and a magnetic recording and reproducing device which perform magnetic recording in a recording medium by increasing the temperature thereof using a light beam, etc., and to a method of performing such magnetic recording.
In the field of optical memory elements, in addition to read-only memories such as the compact disk, recent years have seen the development of recordable memories. Of these, memory elements such as the magneto-optical disk have already been put to practical use.
Such a magneto-optical disk in practical use is a recording medium which uses a perpendicularly magnetized film such as a thin film of a rare earth-transition metal alloy. Information is recorded therein by applying an external magnetic field while projecting laser light thereon. Reproducing from such a magneto-optical disk, on the other hand, makes use of the so-called Kerr effect, in which, when laser light is projected onto the magneto-optical disk, the direction of rotation of the polarization plane of light reflected therefrom changes depending on the presence or absence of recorded information.
With regard to recording and reproducing methods for other types of recording media, one conventional method which has been proposed is a recording and reproducing method for a recording medium made of ferromagnetic material of, for example, CrO2. In this recording and reproducing method, recording is performed by reducing coercive force by projecting laser light onto the recording medium and applying an external magnetic field thereto using a magnetic recording head, and reproducing is performed magnetically using a magnetic reproducing head.
However, in the foregoing recording and reproducing method, since the magnetic reproducing head is used to magnetically reproduce information, information cannot be reproduced from tracks narrower than the width of the magnetic reproducing head (its width in the track width direction, i.e., perpendicular to the track direction).
Therefore, methods such as the following have been proposed for recording and reproducing using tracks narrower than the magnetic head width, and for preventing crosstalk from adjacent tracks.
Japanese Unexamined Patent Publication No. 4-95201/1992 (Tokukaihei 4-95201) discloses a recording and reproducing method using a recording medium made of ferrimagnetic material. In this method, during recording, the temperature of a track of the recording medium to be recorded is increased to the vicinity of its Curie temperature by projecting a light beam along the track, and information is recorded in the track by using a magnetic recording head to apply an external magnetic field thereto. During reproducing, domains opposite the magnetic reproducing head on both sides of a track of the recording medium to be reproduced are heated to the vicinity of the magnetic compensation temperature thereof by projecting light beams onto those domains, and the magnetic reproducing head performs reproducing magnetically.
Further, Japanese Unexamined Patent Publication No. 4-176034/1992 (Tokukaihei 4-176034) discloses a recording and reproducing method using a recording medium made of ferrimagnetic material having a compensation point substantially at room temperature. In this method, during recording, the temperature of a track of the recording medium to be recorded is increased to the vicinity of its Curie temperature by projecting a light beam along the track, and information is recorded in the track by using a magnetic recording head to apply an external magnetic field thereto. During reproducing, magnetization of a domain to be reproduced is increased by projecting a light beam along a track of the recording medium to be reproduced, and a magnetic reproducing head performs reproducing magnetically.
However, in each of the foregoing conventional recording and reproducing methods, due to the influence of a temperature distribution at the recorded bit during recording, the recorded marks are in the form of crescents. For this reason, when using an ordinary magnetic head, increasing linear recording density is likely to lead to crosstalk between adjacent recorded bits in the track direction, and reproducing signal power is also decreased, making accurate reproducing difficult.
A method of resolving the foregoing problems which has been proposed in the past is to perform reproducing using a reproducing head of shape like a crescent. However, manufacture of a crescent-shaped reproducing head leads to further problems, such as complicating the manufacturing process and increasing manufacturing costs.
The present invention was made in view of the foregoing problems with the conventional art, and it is an object hereof to provide a magnetic recording device and a magnetic recording method which are capable of suppressing crosstalk and realizing higher recording density than conventionally. Another object of the present invention is to provide a magnetic recording and reproducing device capable of suppressing crosstalk and realizing higher recording density than conventionally.
(i) In order to attain the foregoing object, a magnetic recording device according to the present invention performs recording using a recording medium having a recording layer made of ferrimagnetic material, and comprises a magnetic head, which applies an external magnetic field to the recording medium during recording; and local temperature increasing means (such as a laser light source), which increase the temperature of the recording medium in a domain thereof opposite the magnetic head but excluding a domain for recording (such as the track to be recorded).
The recording medium made of ferrimagnetic material has a magnetic compensation point, and coercive force increases with increase in temperature. At the magnetic compensation point, residual magnetization is zero, and coercive force is infinite. Accordingly, as specified above, during recording, the local temperature increasing means locally increase the temperature of the domain of the recording medium opposite the magnetic head but outside the domain for recording, so as to give the surrounding domain a greater coercive force than the domain for recording. Then the magnetic head applies to the domain opposite the magnetic head a magnetic field greater than the coercive force of the domain for recording (i.e., its coercive force at room temperature), and smaller than the coercive force in the domain of increased temperature. Thus it is possible to record information accurately in the domain for recording.
At this time, the domain whose temperature is increased by the local temperature increasing means is a domain other than the domain for recording. Accordingly, when recording information using the foregoing magnetic recording device, the temperature distribution rarely extends to the actual domain for recording. For this reason, if the foregoing magnetic recording device is used, the shape of the recorded marks can be made substantially rectangular, thus reducing crosstalk.
Further, since information was conventionally recorded at the Curie temperature, the domain for recording was the area of increased temperature. For this reason, conventionally, the size of the recorded domain was equivalent to the width of the local temperature increasing means (the diameter of a light beam spot, track width of a heater, etc.).
With the present invention, in contrast, since the area whose temperature is increased by the local temperature increasing means is not the actual domain for recording, but the surrounding domain, the size of the domain for recording is not limited by the diameter of the light beam spot.
(ii) In the foregoing magnetic recording device, the domain whose temperature is increased by the local temperature increasing means is preferably made up of domains adjacent to the domain for recording, on both sides thereof.
When the domain for recording is one side of a domain of the recording medium opposite the magnetic head, the domain whose temperature is increased may be a domain adjacent to the domain for recording on one side thereof. However, in this case, the area of increased temperature is larger than when domains on both sides of the domain for recording are heated. For example, if the local temperature increasing means are light beam projecting means, the diameter of the light beam spot must be increased.
When domains on both sides of the domain for recording are heated, in contrast, the diameter of the e.g. light beam spot can be decreased, and the temperature and extent of the domains of increased temperature can be accurately controlled.
(iii) In the magnetic recording device in (ii) above, it is preferable if the local temperature increasing means are light beam projecting means, and if the magnetic head has a width of less than three times a width of each domain of increased temperature adjacent to the domain for recording.
If the width of the magnetic head is set to less than three times the width of each domain of increased temperature adjacent to the domain for recording, the width of the domain not heated, i.e. of the domain for recording, will be less than the width of the local temperature increasing means (the diameter of a light beam spot, width of a heater, etc.). Accordingly, with this structure, recording can be performed in domains narrower than conventionally, without decreasing the size of the magnetic head or the width of the local temperature increasing means (diameter of a light beam spot, etc.). This simplifies manufacture of the magnetic head, and is advantageous in decreasing track width and increasing recording density.
(iv) In the magnetic recording device in any one of (i) through (iii) above, it is preferable if the magnetic head and the local temperature increasing means are both provided on the same side of the recording medium, and if the magnetic head is provided after the local temperature increasing means with respect to a direction of motion of the recording medium.
If the magnetic head and the local temperature increasing means are provided on the same side of the recording medium and the magnetic head is provided after the local temperature increasing means with respect to the direction of motion of the recording medium, the magnetic head can perform recording immediately after heating by the local temperature increasing means. In this case, heating and cooling can be performed efficiently, and spreading of the domain of increased temperature on the recording medium can be suppressed.
(v) In the magnetic recording device of any one of (i) through (iv) above, the local temperature increasing means are preferably light beam projecting means.
By using light beam projecting means as the local temperature increasing means, a narrow domain can easily be increased in temperature. In addition, it is possible to change the width and temperature of the domain of increased temperature by adjusting the power of the light beam. This means that the medium can easily be brought to the same coercive force with high repeatability, which is advantageous in forming equal track widths.
(vi) In order to attain the foregoing objects, a magnetic recording and reproducing device according to the present invention performs recording and reproducing using a recording medium having a recording layer made of ferrimagnetic material, and comprises a magnetic recording head, which, during recording, applies an external magnetic field to the recording medium; and local temperature increasing means for recording (such as a laser light source, heater, etc.), which increase the temperature of the recording medium in a domain thereof opposite the magnetic recording head but excluding a domain for recording.
The recording medium made of ferrimagnetic material has a magnetic compensation point, and coercive force increases with increase in temperature. At the magnetic compensation point, residual magnetization is zero, and coercive force is infinite. Accordingly, as specified above, during recording, the local temperature increasing means locally increase the temperature of the domain of the recording medium opposite the magnetic head but outside the domain for recording, so as to give the surrounding domain a greater coercive force than the domain for recording. Then the magnetic head applies to the domain opposite the magnetic head a magnetic field greater than the coercive force of the domain for recording (i.e., its coercive force at room temperature), and smaller than the coercive force in the domain of increased temperature. Thus it is possible to record information accurately in the domain for recording.
At this time, the domain whose temperature is increased by the local temperature increasing means is a domain other than the domain for recording. Accordingly, when recording information using the foregoing magnetic recording and reproducing device, the temperature distribution rarely extends to the actual domain for recording. For this reason, if the foregoing magnetic recording and reproducing device is used, the shape of the recorded marks can be made substantially rectangular. Accordingly, if the foregoing magnetic recording and reproducing device is used, a signal can be read out from recorded marks recorded in substantially rectangular shape, crosstalk from adjacent recorded bits in the track direction can be suppressed, and accurate recording and reproducing can be performed.
Further, with the foregoing structure, since the area whose temperature is increased by the local temperature increasing means is not the actual domain for recording, but the surrounding domain, the size of the domain for recording is not limited by the width of the local temperature increasing means (the diameter of a light beam spot, etc.).
(vii) The recording and reproducing device in (vi) above preferably also includes a magnetic reproducing head and local temperature increasing means for reproducing, which increase the temperature of the recording medium in a domain thereof opposite the magnetic reproducing head but excluding a domain to be reproduced, to the vicinity of a magnetic compensation temperature thereof.
With this structure, by increasing the temperature of a domain opposite the magnetic head but excluding a domain to be reproduced, information recorded by the foregoing recording and reproducing device can be reproduced with residual magnetization of domains other than the domain to be reproduced substantially at zero. Accordingly, with this structure, even if the width of the magnetic reproducing head is greater than the width of the domain to be reproduced, information recorded in the domain for reproducing can be selectively reproduced, and crosstalk can be reduced.
Further, since recorded marks recorded by the foregoing recording and reproducing device are substantially rectangular, accurate reproducing can be performed using a typical magnetic head, without using a crescent-shaped magnetic head, as conventionally.
(viii) In the recording and reproducing device in (vii) above, it is preferable if the domain whose temperature is increased by said local temperature increasing means for reproducing is made up of domains adjacent to the domain to be reproduced, on both sides thereof, and if the magnetic reproducing head has a width of less than three times a width of each domain of increased temperature adjacent to the domain to be reproduced.
If the width of the magnetic reproducing head is set to less than three times the width of each domain of increased temperature adjacent to the domain to be reproduced, the width of the domain whose temperature is not increased (i.e., the domain to be reproduced) will be smaller than the width of the local temperature increasing means (the diameter of a light beam spot, width of a heater, etc.). Accordingly, with this structure, information can be reproduced from a domain narrower than the width of the local temperature increasing means (the diameter of a light beam spot, etc.), the width of the magnetic reproducing head, etc. This facilitates manufacture of the magnetic reproducing head, and is advantageous in reducing track width and increasing recording density.
(ix) In the magnetic recording and reproducing device in (vii) or (viii) above, it is preferable if the magnetic reproducing head and the local temperature increasing means for reproducing are both provided on the same side of the recording medium, and if the magnetic reproducing head is provided after the local temperature increasing means for reproducing with respect to a direction of motion of the recording medium.
If the magnetic head and the local temperature increasing means are provided on the same side of the recording medium and the magnetic head is provided after the local temperature increasing means with respect to the direction of motion of the recording medium, the magnetic head can perform reproducing immediately after heating by the local temperature increasing means. In this case, heating and cooling can be performed efficiently, and the width of the domain of increased temperature on the recording medium does not become overly large.
(x) In the recording and reproducing device in any one of (vii) through (ix) above, the domain of the recording medium whose temperature is increased by the local temperature increasing means for reproducing is preferably set so as to be larger than the domain whose temperature is increased by the local temperature increasing means for recording.
Domains bordering on the domain for recording are prone to becoming magnetically disordered during recording. With the foregoing structure, since the domain whose temperature is increased by the local temperature increasing means for reproducing is set larger than the domain whose temperature is increased by the local temperature increasing means for recording, information can be reproduced from a domain smaller than the domain for recording. Accordingly, with this structure, by not reproducing domains bordering on the domain for recording, it is possible to perform reproducing of narrow tracks, without influence from the foregoing magnetic disorder.
(xi) In the magnetic recording device of any one of (vii) through (x) above, the local temperature increasing means are preferably light beam projecting means.
By using light beam projecting means as the local temperature increasing means, a narrow domain can easily be increased in temperature. In addition, it is possible to change the width and temperature of the domain of increased temperature by adjusting the power of the light beam. This means that the medium can easily be brought to the same residual magnetization with high repeatability, which is advantageous in always reproducing information from tracks of the same width.
(xii) In order to attain the foregoing objects, a magnetic recording method according to the present invention comprises the steps of (a) increasing a temperature of a recording medium, which has a recording layer made of ferrimagnetic material, in a domain thereof opposite a magnetic head but excluding a domain for recording, and (b) applying to the recording medium an external magnetic field smaller than a coercive force of the domain of increased temperature, and greater than a coercive force of the domain for recording opposite the magnetic head.
The recording medium made of ferrimagnetic material has a magnetic compensation point, and coercive force increases with increase in temperature. At the magnetic compensation point, residual magnetization is zero, and coercive force is infinite. Accordingly, as specified above, by applying a magnetic field smaller than the coercive force in the domain of increased temperature, and greater than the coercive force of the domain for recording (i.e., its coercive force at room temperature), it is possible to record information solely in the domain for recording. In other words, since the external magnetic field applied is less than the coercive force in the domain of increased temperature, recording is not performed in the domain of increased temperature. In the domain for recording opposite the magnetic head, however, the external magnetic field applied is greater than the coercive force in the domain for recording, and thus the magnetization thereof is aligned with the external magnetic field, and recording is performed.
With the foregoing method, the domain whose temperature is increased is a domain other than the domain for recording. Accordingly, with the foregoing method, the temperature distribution rarely extends to the actual domain for recording, and thus the shape of the recorded marks can be made substantially rectangular, thus reducing crosstalk.
(xiii) In the magnetic recording method in (xii) above, the domain whose temperature is increased is preferably made up of domains adjacent to the domain for recording, on both sides thereof.
With this method, by increasing the temperature of domains on both sides of the domain for recording, the domain of increased temperature can be made smaller. For example, when the foregoing local temperature increasing means are light beam projecting means, the diameter of the light beam spot can be decreased, and the domains of increased temperature can be finely controlled.
(xiv) In the magnetic recording method in (xiii) above, it is preferable to heat the recording medium such that the width of each domain of increased temperature adjacent to the domain for recording has a width of more than ⅓ the width of the magnetic head.
If the width of each domain of increased temperature adjacent to the domain for recording is set to more than ⅓ the width of the magnetic head, the width of the domain not heated, i.e. of the domain for recording, will be less than the width of the local temperature increasing means (the diameter of a light beam spot, width of a heater, etc.). Accordingly, with this method, recording can be performed in domains narrower than the local temperature increasing means (diameter of a light beam spot, width of a heater, etc.) or the magnetic head. Accordingly, with this method, track width can be reduced and recording density can be increased.
(xv) In the magnetic recording method in either (xii) or (xiii) above, the temperature increasing step (a) is preferably performed by projection of a light beam.
By performing the temperature increasing step (a) by projecting a light beam, a narrow domain can easily be increased in temperature. In addition, it is possible to change the width and temperature of the domain of increased temperature by adjusting the power of the light beam. This means that the medium can easily be brought to the same coercive force with high repeatability, which is advantageous in forming tracks of equal width.
Additional objects, features, and strengths of the present invention will be made clear by the description below. Further, the advantages of the present invention will be evident from the following explanation in reference to the drawings.